The effect of changes in landscape and habitat complexity resulting from shrub encroachment and climatic factors (aridity and ENSO) on semi-arid ant communities.

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Copyright: Radnan, Gabriella
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Abstract
Changes in complexity affect animal foraging behaviour, inter- and intra-specific competition and predation. Two major drivers of changes in vegetation complexity in Australian drylands are rainfall-driven climate factors (e.g. aridity and the El Nino-Southern Oscillation (ENSO)) and shrub encroachment (the transition of grassland to shrubland). Previous faunal studies have focused on vertebrate communities, but the effects of climate- and encroachment-driven complexity changes on invertebrate assemblages such as ants are poorly known. Ants support a number of critical ecosystem services in drylands such as soil water infiltration, nutrient cycling and seed dispersal. Alterations to ant communities are therefore likely to reduce ecosystem functionality, affecting other biotic assemblages. This thesis examines how climate- and encroachment-driven vegetation changes directly and indirectly structure dryland ant communities and influence ecosystem services such as secondary seed dispersal. Chapter 2 investigates how shrub encroachment, livestock grazing, and soil surface complexity affect ant assemblage and functional group composition, demonstrating that ants are more responsive to disturbances such as grazing than grassland to shrubland transitions. Chapter 3 examines how mammal foraging pit morphology and ant body size influence ant locomotion and seed removal from pits along an aridity gradient. Pit morphology significantly affects ant locomotion by restricting ant movement and their ability to extract seeds, particularly in steeply-sided bettong (Bettongia spp.) pits. Chapter 4 investigates how changes in soil surface complexity affect ant richness, functional group composition, body size and ant activity in grasslands and shrublands. Ants were more responsive to small-scale alterations in soil surface complexity than changes in vegetation community composition associated with a change from grassland to shrubland. Chapter 5 is a long-term study exploring how ant richness and dietary groups respond to productivity changes on two spatial scales (site and dune habitat) and one temporal scale (Climate; ENSO). Ant species richness was greater during La Nina periods and in low-productive environments (desert sites and dune crests). Dietary groups responded positively to ENSO-driven productivity, but the magnitude of their response was dependent on the spatial scale. Chapter 6 summarises my findings and proposes future avenues of research.
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Author(s)
Radnan, Gabriella
Supervisor(s)
Eldridge, David
Gibb, Heloise
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Publication Year
2018
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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